Poor starting

[russ]

Can anyone help? I have been trying to solve a starting & stalling problem with my 05 mercruiser 5.7.
I replaced the carb with a brand new one today and its still doesn't start up without giving it a bit of throttle and will not tick over without stalling until it has fully warmed up. Although its not running as rich as it was with old one on. Could it be electrical or a fuel problem?
Theres an electric module fitted to the side of one the elbows, could this be the cause if faulty?
Any ideas would be appreciated.

 

[rafiki_]

Russ, try a pm to Mercuryman, he knows his way round the Merc engines.

 

[volvopaul]

Can anyone help? I have been trying to solve a starting & stalling problem with my 05 mercruiser 5.7.
I replaced the carb with a brand new one today and its still doesn't start up without giving it a bit of throttle and will not tick over without stalling until it has fully warmed up. Although its not running as rich as it was with old one on. Could it be electrical or a fuel problem?
Theres an electric module fitted to the side of one the elbows, could this be the cause if faulty?
Any ideas would be appreciated.

Sounds like a dirty distributor car, rotor arm etc, I've had this many times and a clean up or renew cap sorts it.

 

[rafiki_]

It could be the auto choke as well VP. These things are very difficult to diagnose from a distance unfortunately.

 

[russ]

New dizzy cap, plugs and rotor earlier this year but the contacts did need cleaning today.
The new carb came with a new choke actuator. Though I had already replaced it recently thinking this was the fault. Engineer had checked it out and it was working within perimeters.
Must be down to electrical due to new carb fitted.
Could oil or temp senders be at fault sending incorrect data to carb? But gauges all work ok.

 

[rafiki_]

New dizzy cap, plugs and rotor earlier this year but the contacts did need cleaning today.
The new carb came with a new choke actuator. Though I had already replaced it recently thinking this was the fault. Engineer had checked it out and it was working within perimeters.
Must be down to electrical due to new carb fitted.
Could oil or temp senders be at fault sending incorrect data to carb? But gauges all work ok.

I don't think the carb is smart enough to read sensor details. Is there an ECU? I would always look for the simplest issues first. How old is the petrol? It loses its "lights" over a period of time, and becomes less easy to ignite. Is the dizzy contact less? Ins there a capacitor in the dizzy? These can break down.

 

[russ]

I don't think the carb is smart enough to read sensor details. Is there an ECU? I would always look for the simplest issues first. How old is the petrol? It loses its "lights" over a period of time, and becomes less easy to ignite. Is the dizzy contact less? Ins there a capacitor in the dizzy? These can break down.

Not sure what the box is on side of elbow, could be an ECU.
No contacts in the dizzy, I'll look to see if there is a capacitor but are they only
fitted if it has points?
I have filled up 3-4 times this year so should be OK although only showing 1/4 tank at the mo.
Just cant think why once warmed up for 20-30 mins she runs fine.

 

[rafiki_]

Sounds more like mixture than anything else, if she runs fine when warmed up. Yep, will only have a capacitor in the dizzy with points, so yours sounds like electronic ignition, no points. Very unlikely to have an ECU with a carb. I think she needs to run a bit richer when cold.

 

[oGaryo]

I seem to recal one of the symptoms of leaky risers being hard starting. Ignition timing out maybe? vacuum leak around the carb?

 

[volvopaul]

It could be the auto choke as well VP. These things are very difficult to diagnose from a distance unfortunately.

I'm not going to get in a debate with you as your not an engineer.

I m just giving russ the my experience as a full time pro as a marine engineer.

I will let you take over the diagnosis.


From a distance!!!

 

[rafiki_]

I'm not going to get in a debate with you as your not an engineer.

I m just giving russ the my experience as a full time pro as a marine engineer.

I will let you take over the diagnosis.


From a distance!!!

Actually Paul I am an Engineer.

 

[aquapower]

I remember a few years back I had a Volvo V8 with similar symptoms, it was the corroded riser problem and had let the salt water corrode the valves, try a compression test, this can tell you a lot.
Why was the new carb fitted? Was it to eliminate this same problem?

 

[russ]

I remember a few years back I had a Volvo V8 with similar symptoms, it was the corroded riser problem and had let the salt water corrode the valves, try a compression test, this can tell you a lot.
Why was the new carb fitted? Was it to eliminate this same problem?

As it seemed to be running too rich when cold and poor starting and I couldn't adjust the mixture I assumed it was a carb problem. Earlier in year i sprayed carb cleaner in and ran up the engine for a while at high revs this seemed to of helped a little.
Do you think the plugs maybe coked up as it has been running too rich and therefore a weak spark until hot?


"I seem to recal one of the symptoms of leaky risers being hard starting. Ignition timing out maybe? vacuum leak around the carb?"

Thanks oGaryo, I'm by no means a mechanic but if it runs fine when hot can the timing be out?
The only pipe other than fuel line to the carb is the PCV pipe but no vacuum pipes. New carb gaskets fitted as well so shouldn't be a leak.
If I pump throttle a few times and leave it at 1/4 setting it will start but not tick over.

 

[volvopaul]

As it seemed to be running too rich when cold and poor starting and I couldn't adjust the mixture I assumed it was a carb problem. Earlier in year i sprayed carb cleaner in and ran up the engine for a while at high revs this seemed to of helped a little.
Do you think the plugs maybe coked up as it has been running too rich and therefore a weak spark until hot?


"I seem to recal one of the symptoms of leaky risers being hard starting. Ignition timing out maybe? vacuum leak around the carb?"

Thanks oGaryo, I'm by no means a mechanic but if it runs fine when hot can the timing be out?
The only pipe other than fuel line to the carb is the PCV pipe but no vacuum pipes. New carb gaskets fitted as well so shouldn't be a leak.
If I pump throttle a few times and leave it at 1/4 setting it will start but not tick over.

Are we def talking about a carb engine, which carb? 4 barrel Holley or a quadrajet , if it won't run at idle then it sounds like the slow run jet is partially blocked or the idle screw/ air ratio screw is either not adjusted correctly or it's passage from the fuel bowl to the idle jet is not allowing fuel to it or hough the passage in order to supply a fuel mixture at low vacuum rpm.

 

[russ]

Are we def talking about a carb engine, which carb? 4 barrel Holley or a quadrajet , if it won't run at idle then it sounds like the slow run jet is partially blocked or the idle screw/ air ratio screw is either not adjusted correctly or it's passage from the fuel bowl to the idle jet is not allowing fuel to it or hough the passage in order to supply a fuel mixture at low vacuum rpm.

Def a 2 barrel carb, changed it myself yesterday. Model 3310-866143A03. Pics attached are the old one. Exact same as new one.
Unusual that I cant see a mixture screw and that it only has butterflies at base of carb and none at the top.

 

[ARA]

I had a boat with an AQ211, it was always bad on cold start up & seemed to chug & chug with the smell of petrol for the first 5 minutes & then cleared. The engineer cable tied the automatic choke so that it didn't work. Cold starts were performed by openeing and closing the throtlle 3 to 4 times & then once fired kept the revs slightly above 1000 revs.

 

[russ]

I had a boat with an AQ211, it was always bad on cold start up & seemed to chug & chug with the smell of petrol for the first 5 minutes & then cleared. The engineer cable tied the automatic choke so that it didn't work. Cold starts were performed by openeing and closing the throtlle 3 to 4 times & then once fired kept the revs slightly above 1000 revs.

I do the same but didn't want sit fettling the throttle until warm for 20 mins. I don't have any petrol fumes though.
Must be reason why two carbs are acting the same.

 

[talltim]

I agree with VP I'd be looking towards either a blocked idle jet, float chamber vent or needle valve?

IIRC the float chamber on US spec engines/boats is vents by a pipe/hose to the air filter so as to contain fumes, worth checking that this pipe is not blocked or restricted.

I would also recheck the float level

Hope this helps

 

[talltim]

No butterfly's at the top of marine carbs as no choke fitted

 

[russ]

I agree with VP I'd be looking towards either a blocked idle jet, float chamber vent or needle valve?

IIRC the float chamber on US spec engines/boats is vents by a pipe/hose to the air filter so as to contain fumes, worth checking that this pipe is not blocked or restricted.

I would also recheck the float level

Hope this helps

But its a new carb with factory settings.